Screw air compressors



Oct. 18, 1966 v cg N us 3,279,682

SCREW AIR COMPRESSORS Filed Feb. 20, 1964 4 Sheets-Sheet 1 Inventor HANSB0235 VAeEmus Attorney 1966 H. B. VAGENIUS SCREW AIR COMPRESSORS 4Sheets-Sheet 2 Filed Feb. 20, 1964 I HANs B01235 VAG'ENIUS Wmffimmif$Attorney Oct. 18, 1966 H. B. VAGENIUS 3,279,682

SCREW AIR COMPRESSORS Filed Feb. 20, 1964 4 Sheets-Sheet s Inventor HANsB0231; VAGEN lus A tlorney Oct. 18, 1966 H. B. VAGENIUS 3,279,682

V SCREW AIR COMPRESSORS Filed Feb. 20, 1964 4 Sheets-Sheet 4 F/GG.

' Inventor HAN 5 E0235 VAG-EN Ms W 330mm Attorney United States Patent3,279,682 SCREW AIR COMPRESSORS Hans B. Vagenius, Glasgow, Scotland,assignor to James Howden & Company Limited, Glasgow, Scotland, a Britishcompany Filed Feb. 20, 1964, Ser. No. 346,275 Claims priority,application Great Britain, Feb. 23, 1963, 7,372/ 63 3 Claims. (Cl.230158) This invention relates to machines of the kind having coactingrotors for effecting compression or expansion of a fluid, workingmedium. Such machines are normally used as air compressors and will bedescribed hereinafter and in the claims as such.

Screw air compressors are well known which comprises two interactingrotors, a male rotor and a fem-ale rotor, in a common casing. The malerotor is formed with a series of helical lobes which engagecorresponding helical lands in the female rotor. There may be, forexample, four lobes on the male rotor and six lands on the female rotor,though any suitable numbers of lobes and lands may be used. Consideringone such land in the female rotor, air is admitted through an inlet portand completely fills the land. As the rotors rotate, the inlet port isclosed and the point of engagement between the land and thecorresponding lobe on the male rotor moves along the land thuscompressing the air trapped in the land by the casing, the air beingreleased when the outlet port is reached. If, for design reasons, it isdifiicult or ineflicien-t to compress the air to the desired pressure ina single stage, two compressor stages may be provided in tandem. It hasalso been proposed to inject oil into the compressor both to absorb theheat of compression and to im prove the sealing between the rotors.

The present invention provides a screw air compressor having two stagesin tandem, each stage comprising interacting male and female rotors, andin which two rotors, one from each stage, are mounted on a common shaft,said shaft being supported on only two bearings of which one is mountedat each end of the first stage.

The present invention also provides a screw air compressor having twostages in tandem, each stage comprising interacting male and femalerotors, and in which the second stage rotors have a diameter differentfrom that of the first stage rotors.

Embodiments of the invention will now be described, by way of example,with reference -to the accompanying drawings, in which:

FIGS. 1 and 2 are respectively sectional vational views of a firstembodiment;

FIG. 3 is a sectional plan view of a second embodiment;

FIGS. 4 and 5 diagrammatically illustrate the two embodiments of FIGS. 1to 3;

FIGS. 6 and 7 diagrammatically illustrate modifications of theseembodiments; and

FIG. 8 diagrammatically illustrates another modification of theinvention. I

Referring now to FIGS. 1 and 2, an oil-injected tandem, screwair-compressor 10 according to the invention, is provided with twoparallel shafts 11 and 12. On the first shaft 11 is provided the malerotors 13 and 14 of the first and second stages 15 and 16 respectively,the rotors being provided with the helical formations 17 and 18 that arewell known in the art. The male rotor 13 of the first stage 15 is formedintegral with the shaft 11 and its lobe formation 17 has a right handedhelix whereas the male rotor 14 of the second stage 16 is keyed orotherwise secured to the shaft 11 and its formation 18 has a lefthandedhelix. On the second shaft 12 are provided the plan and elefemale rotors19 and 20 of the two stages 15 and 16, the female rotors being formedwith similar helical land formations 21 and 22 and engaging theircorresponding male rotors. It should be noted that the land formation 22of the second stage female rotor 20 again has an oppositely directedhelix fromthe first stage, female rotor 19 and again is formedseparately from the shaft 12. It may, however, be secured to the shaftor it may be free to move circumferentially around the shaft 12.

A casing encloses the shafts and rotors to allow a minimum clearancearound the rotors and consists of a main casing 25, a secondary casing26 and an end casing 27. The main casing 25 extends from the outer endof the first stage rotors 13 and 19 to the inner end of the second stagerotors 14 and 20, the secondary casing 26 is secured by bolts 28 to oneend of the main casing 25 and encloses the second stage rotors 14 and20, and the end casing 27 is secured to the other end of the main casing25 and covers the exposed ends of the first stage rotors 13 and 19.

The two shafts 11 and 12 are similarly mounted in bearings in thecasing, a first bearing 30 being provided at the end of each shaftremote from the second stage and a second bearing 31 being providedbetween the two stages i.e. bearings are provided at each end of thefirst stage rotors 13 and 19.

An inlet port 35 is provided in the casing adjacent the first bearings30, i.e. remote from the second stage, to allow air to enter the firststage of the compressor and passages 36 are provided in the casing topass the air from the outlet 37 of the first stage adjacent the secondbearings 31 to the inlet 38 of the second stage which is at the ends ofthe second stage rotors 14 and 20 remote from the first stage. Theoutlet 39 from the second stage is thus also adjacent the second bearing31 and an outlet port 40 is provided there in the casing.

In the embodiment illustrated, the port 40 is provided in the maincasing 25 but it could equally well be provided in the secondary casing26.

Byproviding the outlet or high pressure ends of both stages at oppoisngends thereof, the thrusts on the shafts 11 and 12 due to the pressuredifferentials between the ends of the rotors act in opposite directionsand are largely balanced out. The bearings 30 and 31 are basicallyjournal bearings which may be designed to absorb the small resultantaxial thrust.

As the second bearings 31 are provided adjacent the high pressure endsof the rotors, there is little deflection of the shafts 11 and 12 atthis point and this leads to improved performance and ease ofmanufacture as the clearances, both axial and radial, between the casingand the high pressure ends of the rotors are critical.

Although, as decsribed hereinbefore, the second stage rotors 14 and 20,which are short compared with the first stages at opposing ends thereof,the thrusts on the shafts from the outlet end of the first stage, theembodiment could be modified by providing the overhung shafts at theinlet end of the first stage.

Moreover, one of the second stage rotors may be split transversely asindicated at 50 and the two parts thereof, 50 and 51, locked togetherwith a slight angular displacement thus adjusting and mitigating theback lash between the two male and female rotor systems.

The oil injection could be dispensed with or replaced, by, for example,water injection. If a lubricant is not injected into the compressor,timing gears are necessary between the male and female rotors, andmoreover the air is passed between the two stages through an intercoolerwhich may be external or integral.

In FIG. 3 of the accompanying drawing is shown another embodiment of theinvention, and, as it is similar to the embodiment of FIGS. 1 and 2,corresponding parts carry corresponding reference numerals. Again, thecompressor shown in FIG. 3 comprises two male rotors 13 and 14 on acommon shaft 11 which is mounted in bearings 30 and 31 in a casingconsisting of the three parts 25, 26 and 27. The first stage femalerotor 19 is mounted on the shaft 12. However to allow for a higherinterstage pressure and therefore a higher overall pressure ratio, thesecond stage rotors 14 and 20 have a diameter that is different from thediameter of the first stage rotors 13 and 19' and therefore the secondstage female rotor 20 is not overhung on the shaft 12 but is providedwith its own shaft 55 mounted in bearings 56 and 57.

The modifications'described hereinbefore with regard to the embodimentof FIGS. 1 and 2 are also applicable to the embodiment of FIG. 3.

It is also possible the interchange the male and female rotors of thesecond stage for both the embodiments described hereinbefore, this beingdiagrammatically illustrated in FIGS. 4 to 7, Of which FIGS. 4 and 5illustrate the embodiments hereinbefore described and- FIGS..6 and 7illustrate the embodiments with the second stage rotors interchanged.

In FIG. 8 further modification is illustrated in which the free-runningsecond stage rotor is mounted on bearings on a stationary shaft.

I claim:

1. A screw compressor comprising a casing, side-by-side shafts rotatablymounted in the casing, and two pairs of 4 side-by-side interacting maleand female rotors mounted on the shafts in tandem and co-operating withthe casing, to provide two compression stages, wherein the outlets ofboth stages are located at opposing ends of the rotor pairs, 7 and atleast one of the shafts carries two rotors namely one from each stage,and is supported on only two bearings one at each end of one of therotors so that the other rotor is overhung.

2. A screw compressor according to claim 1, wherein the casing is in twodetachably interconnected ,parts enclosing the respective pairs ofrotors.

3. A screw compressor according to claim 1, wherein the rotors of onepair are of a different diameter from the rotors of the other pair.

References Cited by the Examiner UNITED STATES PATENTS MARK NEWMAN,Primary Examiner. WILBUR J. GOODLIN, Examiner.

1. A SCREW COMPRESSOR COMPRISING A CASING, SIDE-BY-SIDE SHAFTS ROTATABLYMOUNTED IN THE CASING, AND TWO PAIRS OF SIDE-BY-SIDE INTERACTING MALEAND FEMALE ROTORS MOUNTED ON THE SHAFTS IN TANDEM AND CO-OPERATING WITHTHE CASING, TO PROVIDE TWO COMPRESSION STAGES, WHEREIN THE OUTLETS OFBOTH STAGES ARE LOCATED AT OPPOSING ENDS OF THE ROTOR PAIRS, AND ATLEAST ONE OF THE SHAFTS CARRIES TWO ROTORS NAMELY ONE FROM EACH STAGE,AND IS SUPPORTED ON ONLY TWO BEARINGS ONE AT EACH END OF ONE OF THEROTORS SO THAT THE OTHER ROTOR IS OVERHUNG.